Structural, electronic, and optical properties of medium-sized Lin clusters (n=20, 30, 40, 50) by density functional theory

The lowest-energy structures of medium-sized Lin (n=20, 30, 40, 50) clusters are determined from simulated annealing technique followed by geometry optimization within the framework of density functional theory. The shapes of magic-number Li20 and Li40 clusters are nearly spherical while those of the other clusters are ellipsoid. The growth of Lin clusters is based on core of multi-layered pentagonal bipyramids with other atoms capped on the surface. The binding energies of the Lin clusters were computed and compared with experiments. At magic-number sizes (n=20, 40), Lin clusters possess relatively larger HOMO–LUMO gaps and higher ionization potentials, corresponding to the closure of electron shell. The molecular orbitals of the lithium clusters can be grouped into electron shells and their spatial distributions resemble the atomic orbitals. The average polarizability of the Li clusters reduces rapidly with cluster size and can be approximately described by a classical metallic sphere model. The optical absorption spectra of Lin clusters from time-dependent density functional theory calculations show giant resonance phenomenon, and resonance peak blueshifts with increasing cluster size.